After Senator Pratt's call with Director Karaway, he understood that since Peter and his team had already found the location of the evidence box, they would definitely go to retrieve it as soon as possible. He was also very concerned about what exactly the evidence in that box was.
Even though he was already a senator, any problems related to his previous cases could very well end his political career completely.
After talking with Peter, Director Karaway requested Peter to form a team to search for the evidence, asking the bureau to get it first. But in reality, she was merely saying that, mostly looking to delay Peter and his team's progress.
Before the investigation, when Peter met with Hughes, Hughes said a few very important words to him, "You are the law. Senator Pratt is dirty. Pratt and Karaway are obstructing justice. What you need to do is to fight back, take them down."
